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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

326

BENZOLES

For exact determinations, the hydrocarbons remaining suspended in the
sulphuric acids employed should be collected. The acid liquors are poured
slowly and with shaking on to an equal weight of pounded ice in a flask, the
temperature never exceeding 40°. The liquid thus obtained is distilled and
the oil separating at the surface of the first 50 c.c. of distillate added to the
quantity determined directly. The total oil thus obtained is repeatedly purified
with fuming sulphuric acid (20% of anhydride) in lots of 30 grams each until
no further diminution in volume takes place. It is then washed with water
and measured, the volume, divided by 2, giving the quantity of paraffin hydro-
carbons in 100 of the benzole.

(a!) NAPHTHALENE. 10 c.c. of the benzole are allowed to evaporate
spontaneously in a glass dish, any naphthalene present remaining crys-
tallised on the walls of the dish.

5. Degree of Refining.—Benzoles may contain larger or smaller quan-
tities of resinous substances not completely removed by refining. The
presence of these substances may be detected as follows :

(a) WITH SULPHURIC ACID. 5 c.c. are added to 5 c.c. of cone, sul-
phuric acid in a cylinder with a ground stopper, the mixture being shaken
for two or three minutes and the colour of the acid observed. Pure pro-
ducts do not colour the acid at all, and commercial products colour it pale
yellow or brown according to the extent to which refining has been carried.
The coloration may be measured by comparison with solutions of potassium
dichromate in sulphuric acid.

(6) WITH BROMINE. 5 c.c. of the benzole are mixed in a beaker
with 10 c.c. of dilute sulphuric acid (1:5) and a decinormal potassium
bromide and bromate solution (9-9167 grams KBr + 2-7833 grains KBr03
per litre) run in, slowly and with shaking, at intervals of five minutes until
the bromine liberated no longer undergoes absorption; this is shown by
the orange-yellow coloration of the benzole and by the blue colour imparted
to starch-iodide paper. The degree of refining is in inverse ratio to the
amount of bromine absorbed (i c.c. N/io-solution = 0-008 gram Br). The
loss during further refining will be i% per 0-2 c.c. of the bromine solution
used.

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* *

The benzoles most commonly found on the market may come from the dis-
tillation of light tar oils or from the distillation of the washing oils obtained
by exhaustion of the gas from the manufacture of coke or coal gas by means
of heavy oils. These are mixtures in varying proportions of benzene and higher
homologues. Examples of the more important characters of these products
are as follows (Spilker) :ulpho-acids (Kraemer and Spil-